1. Field of the Invention
This invention relates to diaphragms for use in pumps and valves, and more particularly to a diaphragm including a solid polytetrafluoroethylene layer and an integral attachment stud.
2. Background Information
Diaphragm pumps are used in pumping a wide variety of materials especially when the materials are abrasive, have high viscosity, or consist of slurries that might damage other pump designs. These pumps are often air driven which is advantageous in pumping flammable liquids or in environments where electrically driven equipment could otherwise be hazardous. However, electrically or otherwise mechanically driven designs also find wide utility. Due to the wide range of different materials these pumps are used to move, a correspondingly wide variety of materials are used in the pump construction. These include plastics and metals. For the same reason the critical driving member, i.e., the pump diaphragm, typically must be manufactured from a variety of materials.
Chemically resistant layers, such as those made of polytetrafluoroethylene (PTFE), are widely used in industry to protect sensitive parts of machinery or equipment from the corrosive effects of acids or other chemicals. One such use is in two piece pump diaphragms commonly used with air or electrically driven diaphragm pumps. In the two piece diaphragms, an outer PTFE overlay diaphragm is commonly used to protect an inner rubber diaphragm from materials that would cause rapid failure of the rubber part alone. In other cases, the PTFE provides the sole material of construction of the diaphragm.
In some applications, it is desirable to provide a diaphragm having a centrally disposed stud instead of an aperture, for securing the diaphragm to the operative portion of the pump. These studs are generally fastened to the diaphragms mechanically, such as by passing the stud through a central aperture of the diaphragm and securing it by threaded fasteners, etc. This approach, however, tends to provide a working face of the diaphragm that is uneven. Moreover, the hole in the center of the diaphragm through which the shaft extends, is a potential source of leakage and the fastener and/or washer presents a geometry which is difficult to clean for sanitary applications, such as food processing. In particular, this construction provides crevices and the like between the stud (and/or fastener) and the diaphragm which tend to collect the pumped material and also provides points of germination for corrosion and abrasion, etc.
One attempt to overcome these drawbacks has been to bond the stud directly to the diaphragm without passing the stud through the diaphragm, so that a substantially smooth, uninterrupted working face is provided.
One technique for providing such an integrated stud has been to bond the stud directly to the PTFE diaphragm. However, such techniques have generally been unsatisfactory due to the difficulty of forming a secure bond to PTFE. Another approach has been to mold the stud in-situ with the PTFE diaphragm, and subsequently use machining techniques to provide the diaphragm with the requisite physical dimensions. While this approach may be satisfactory when fabricating diaphragms of relatively small sizes, i.e. less than approximately 2 inches (5 cm) in diameter, this approach has generally been undesirable for use with larger sized diaphragms due to the amount of material waste and relatively high manufacturing costs associated with the machining techniques. Moreover, it is generally difficult to produce large thin molded shapes having relatively large surface area and desired material density without cracks.
In a still further approach, in the case of the aforementioned two piece diaphragms, the difficulty associated with bonding a stud directly to PTFE has been circumvented by bonding the stud directly to the non-PTFE (i.e. rubber) layer. While this approach may operate reasonably satisfactorily in some applications, this approach tends to delaminate the rubber layer from the PTFE layer due to the lack of direct bond between the stud and the PTFE layer.
Thus, a need exists for an improved PTFE pump diaphragm and method of manufacture thereof, having an integral stud to eliminate the need for a central through-hole and the potential leak/contamination source generated thereby.